Trees are more than a pretty addition to our landscape: they make the environment cleaner and more comfortable. In the summer, trees provide shade; in winter, they offer shelter from harsh winds. Correctly placed shade trees, windbreaks, and foundation plantings can reduce heating and cooling costs by an estimated 25 to 30 percent or more. Tree canopies keep the ground-level air temperature cool, lowering air pollutant levels when summer temperatures are cool.
Winter Heating Considerations
Both sun and wind affect home temperatures in winter.
- The sun creates a lot of solar energy by shining through east and west windows and south windows in the winter when the sun is low in the sky.
- Solar energy can generate as much as 5 to 20 percent of the energy needed to heat a home.
- Warm air escaping, along with cold wind entering a home, increases heating costs and accounts for 25 to 40 percent of heating requirements.
- The stronger the wind, the colder the temperatures, the greater the effect.
Summer Cooling Considerations
- Insulation in the roof and walls prevents most solar energy from entering a home.
- Sun shining through windows generates approximately half of a home's unwanted heat during summer. Almost twice as much solar energy enters through east and west windows as south windows because the summer sun is high in the sky.
How Trees Help
When planting trees for energy conservation, try to:
- Create windbreaks to block harsh winter winds, but allow cool summer breezes to flow through.
- Increase the tree canopy to cool the surface area.
- Shade east and west windows in the summer, where most solar energy enters the house.
- Avoid shading south windows in winter, where most solar enters the house.
In most places, winter winds come from a different direction than cool summer breezes. Placing an effective windbreak along the side of the house where winter winds are strong can provide shelter from cold winds and reduce heating energy needs.
Planning a Wind Break
An area of relatively calm air is formed downwind from a windbreak, a distance of approximately 10 times the height of the windbreak. There can be wind reduction as much as 25 times the height of the windbreak downwind.
To be effective, the windbreak should consist of trees and shrubs that are tall, dense, and in a long enough line to protect the house. The most efficient windbreaks consist of at least one row of dense evergreen trees whose branches extend to ground level. Usually the windbreak is planted in rows perpendicular to the wind direction. In most cases, the windbreak runs north and west of the building. A windbreak that permits 50 to 60 percent of the wind to penetrate (such as evergreen trees) is better than a solid barrier (such as a solid fence) because it creates a larger area of protection on the downwind side.
enlargePlanning a Windbreak
Some small residential yards don't have space for large evergreen trees, but a canopy of tall, deciduous trees provide a lot of shelter. For the greatest effect, mature trees should cover at least half the canopy space. This provides shelter from winter winds and a significant amount of shading from summer sun.
enlargeProper Shading Techniques
enlargeShrubs Can Provide Insulation
Planning for Solar Heat Savings
To prevent solar heat in summer, the best place to plant is west and east of windows. Planting trees on a home's south side offers less shade where needed in summer and does not prevent solar heating in the summer.
In addition to shading the house, tree plantings should provide shade to air conditioners, parking places and paved areas in summer. Shade allows an air conditioner to run more efficiently and prevents heat build-up in cars and on pavement.